A battery cell has been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. One type of battery cell is known as the lithium-ion battery. The lithium-ion battery is rechargeable and can be formed into a wide variety of shapes and sizes so as to efficiently fill available space in electric vehicles. For example, the battery cell may be prismatic in shape to facilitate a stacking of the battery cells. A plurality of individual battery cells can be provided in a battery pack to provide an amount of power sufficient to operate electric vehicles.
Typical prismatic battery cells have a pair of plastic coated metal layers fused around a periphery of the battery cell in order to seal the battery cell components. The sealing of the battery cells generally begins with providing one of the plastic coated metal layers with a cavity, sometimes called a “butter dish” shape. The battery cell components are disposed inside the cavity of the plastic coated metal layer. The other of the plastic coated metal layers is then placed on top of the battery cell components and fused at the periphery to the one of the plastic coated metal layers with the cavity, for example, by heat sealing around the edges. The battery cell for incorporation in a battery pack assembly is thereby provided.
Battery cells such as lithium-ion battery cells are known to generate heat during operation and as a result of a charge cycle when recharging. When overheated or otherwise exposed to high-temperature environments, undesirable effects can impact the operation of lithium-ion batteries. Cooling systems are typically employed with lithium-ion battery packs to militate against the undesirable overheating conditions. The cooling systems may include cooling plates or fins sandwiched between individual battery cells within the battery pack. The cooling system may have channels through which a coolant flows in a heat transfer relationship with the battery cells. Nonlimiting examples of known cooling systems for battery cells are described in Assignee's co-pending U.S. patent application Ser. No. 12/713,729 to Essinger et al. and U.S. patent application Ser. No. 12/842,478 to Kumar et al., the entire disclosures of which are hereby incorporated herein by reference.
Conventional cooling systems have included air to air cooling, cooling plates or fins sandwiched between individual battery cells within the battery pack along with heat sinks in the same location.
There is a continuing need for a battery cooling system and a method for making the battery cooling system that maximizes efficient heating and cooling of the battery cells with minimum delta temperatures. Desirably, the battery cooling system and method maintains uniform surface temperatures over the battery cells and efficiently transfers heat away from the cells using open bath cooling in a hybrid vehicle.